1. Field of the Invention
This invention relates to an apparatus and method for reading an image, and particularly to an image reading apparatus and method for reading from above a document so mounted as to show its face upwardly.
2. Description of Related Art
Among conventional image reading apparatuses is counted one that is adapted to detect the boundary between a document placed on a document stand and the face of the document stand and yield as an output an image of the document less the area irrelevant thereto.
When such a document as a book of appreciable thickness (hereinafter referred to as "book document") is opened at a page containing a relevant image and this book document is read in the apparatus of the principle mentioned above, however, since this apparatus inevitably reads the lateral parts of the page opposed across the image part of the book document additionally as part of the document, the image yielded contains the irrelevant image of such lateral parts of the page and offers an unpleasant appearance.
As an approach to the elimination of the image of such lateral parts of the book document for the purpose of improving the appearance of the yielded image, JP-A-06-3,236,865, for example, discloses an image reading apparatus which is adapted to effect the elimination of the image of lateral parts of the document by discerning the area of lateral parts of the document in virtue of the fact that the luminance of the lateral parts of the document is lower than that of the face part of the document.
The image reading apparatus resorting to the principle of reading from above a book document which is mounted as opened upwardly, however, has the problem of encountering difficulty in discerning between a difference of luminance due to a curve in the face part of a document and a difference of luminance between the face part of a document and the lateral part of a document because the face part of the document is curved.
Further, when the part of the face of the document which borders on the lateral faces of the document happens to contain an index, a pattern of black frame, or a black background, the apparatus has the problem of failing to discern satisfactorily between such special marks and the lateral parts of document.